Here is the full list of all 28 Alekhine's Gun achievements.
Obtain all disguises in the game
Obtain all trophies
Hide 30 bodies
Obtain Maniac Ranking on a level
Use chloroform on 30 enemies
Garrote 30 enemies
Complete the game without killing except for assassination targets
Obtain Ghost Ranking on all levels
Complete level 11
Complete level 10
Complete level 9
Complete level 8
Complete level 7
Complete level 6
Get 30 Headshots
Complete level 5
Perfect lockpicking attempt on a lock with at least 4 locking mechanisms
Complete level 4
Complete level 3
Perform a perfect rewiring during a sabotage puzzle
Complete a level using one disguise or less
Complete level 2
Complete a level without using your gun
Obtain Ghost Ranking on a level
Complete all assassinations in a level using only accidents
Complete a level without killing except for assassination targets
Complete a level without using Instinct Mode
Complete level 1